The present invention relates to an ultrasonic probe of an ultrasonic apparatus for acquiring information from inside of an object to be inspected and discriminating a structure or a tissue included in the object to be inspected on the basis of the acquired information, and relates to an ultrasonic inspection apparatus using such an ultrasonic probe.
Conventionally, it has been conducted in the medical and nondestructive inspection fields to transmit an ultrasonic wave into an object to be inspected, measuring an echo signal reflected within the object to be inspected or an ultrasonic wave transmitted through the object to be inspected, and discriminate a structure or a tissue included in the object to be inspected. In such an ultrasonic apparatus, an ultrasonic probe is used to transmit an ultrasonic wave to the object to be inspected and receive a signal brought about by the object to be inspected.
An ultrasonic wave is generated by applying a voltage of approximately 400 V to electrodes of piezoelectric elements included in the probe. It is known that continuously applying a voltage to the electrodes with a certain specific frequency causes an ultrasonic wave having the resonant frequency to be generated whereas applying a voltage in a pulse form causes an ultrasonic wave having a certain band around a center frequency equivalent to a resonant frequency of the piezoelectric elements to be radiated from the probe.
If an ultrasonic wave transmitted or received by a conventional probe is subjected to frequency analysis, only one signal having the resonant frequency of the piezoelectric elements is obtained as a high gain signal.
In the object to be inspected, the ultrasonic wave is attenuated more strongly as the region to be inspected becomes becomes deeper. And the attenuation ratio becomes greater as the frequency of the ultrasonic wave is made higher. In an apparatus for imaging a signal obtained from the inside of the object to be inspected such as an apparatus used for medical image diagnosis, the spatial resolution of an obtained image becomes better as the frequency of the ultrasonic wave is made higher. In other words, a favorable image of a shallow region of the object to be inspected is obtained by using a probe having a high ultrasonic frequency.
If a probe having a high frequency is used to inspect a deep region, however, the ultrasonic wave is attenuated and a sufficient receiving sensitivity is not obtained. Eventually, a probe having a low ultrasonic frequency must be used for a deep region at the sacrifice of the spatial resolution. It was thus difficult to measure favorable signals from both a deep region and a shallow region of an object to be inspected simultaneously by using a single probe. In an adopted method, therefore, probes are used properly in a deep region and a shallow region of the object to be inspected in order to obtain images respectively. In this case, it is difficult to apply those probes to completely the same position of the object to be inspected and obtain images of the same region. In the case where the object to be inspected is a living body, organs and tissues within the living body move while probes are being exchanged. Even if the probes can be applied to the same region, therefore, it is difficult to obtain temporally the same image and the inspection efficiency is disadvantageously poor. Thus various attempts to widen the bandwidth of the probe have been made. Under the existing conditions, the width expansion as compared with the conventional probe is limited to a slight value.